The purpose of this work was to identify organo-selenium and organo-tellurium
compounds produced by genetically modified Escherichia coli cells that
were amended with selenium or tellurium salts. The goals of this research were
to see which genetic modifications were responsible for the production of the
organo-chalcogen compounds. Experiments were designed to detect new, never previously
reported compounds above the modified E. coli cultures.

Experiments were also performed to see if the change from aerobic to anaerobic
growth conditions affected the bioremediation potential of Pseudomonas fluorescens
K27. Recombinant E. coli cultures were amended with either tellurate,
tellurite, selenate, or selenite or some combination of these salts. Experiments
show that ORF 600 and 1VH (which contains ORF 600) produce organo-tellurium
and organo-selenium compounds. Expression of ORF 600, which contains the gene
encoding for a UbiE methyltransferase, resulted in production of organo-tellurium
compounds when the clone was amended with tellurate but did not produce any
organo-tellurium compounds when the clone was amended with tellurite.

Organo-tellurium compounds that were detected above tellurium amended cultures
were dimethyl telluride, methanetellurol, dimethyl tellurenyl sulfide, and dimethyl
ditelluride. The last three have never been reported before in the literature
as bacterial products. Organo-selenium compounds that were detected were dimethyl
selenide, dimethyl selenenyl sulfide, dimethyl diselenide, and dimethyl selenodisulfide.
The oxidation state of selenium in the amendments did not affect the production
of organo-selenium compounds.

Dimethyl selenodisulfide has never been detected in the headspace gases above
bacterial cultures but was determined here; its structure was confirmed by GC/MS
and compared to a similar mass spectrum found in the literature.

Detection of these volatile compounds was performed by using either gas chromatography-sulfur
chemiluminescence detection or gas chromatography-mass spectrometry.

Sequentially switching from aerobic to anaerobic growth did not show any improvement
or decline of the bioremediation potential of Pseudomonas fluorescens
K27. Measurement of dissolved oxygen (D.O.) content of the culture media was
done by a D.O. probe that measured the percent of oxygen saturation in the solution.
A D.O. probe that measured the solution phase concentration of dissolved oxygen
(mg/L) was also used.